Abstract
The basin-forming process along a convergent margin off the eastern coast of Eurasia was pursued on the basis of geological, geochemical, and geophysical approaches. Central Hokkaido has been a site of vigorous tectonic events throughout the Cenozoic reflecting the long-standing subduction of oceanic plates in the region. Geochemical modeling provided an estimate of the eroded Paleogene unit in the study area. Data on the considerable thickness of the missing unit implied continued subsidence of the forearc region and its subsequent exhumation under the emergence of a compressive regime synchronous with the back-arc opening stage. Spatially large facies variety in the Paleogene system suggests that basin compartmentalization occurred as a result of the trench-parallel component of the plate convergence. Right-lateral motion seems to have been the dominant type in Hokkaido and the forearc of northeast Japan since the Late Cretaceous, except for a left-lateral episode during rapid subsidence of the Izanagi Plate around 110 Ma. Numerical modeling demonstrated that dextral slip on a bunch of longitudinal strike-slip faults restored the Neogenedepocenters in central Hokkaido, together with an east-west compressive regime related to an arc-arc collision.
Highlights
Hokkaido is an island presently located at a junction of the Kurile arc and northeast Japan arc (Figure 1)
As for the trench side of the forearc region, modeling results clearly indicate that subsurface temperatures determined for the present thickness of the analyzed rock units did not match those of the measured maturation levels
We assumed that the Maastrichtian Hakobuchi Formation, the stratigraphic age of which is based on the unit distributed to the south of the study area (Sakai and Kanie 1986), was deposited on the studied section because it was the uppermost member of the Yezo forearc basin described by Ando (2003)
Summary
Hokkaido is an island presently located at a junction of the Kurile arc and northeast Japan arc (Figure 1). Reflecting active deformation on the Eurasian margin, voluminous and various types of sedimentary basins have emerged in the island through the Cenozoic. This region is an example of basin evolution controlled by the transition of tectonic regimes. Compared to monotonous fine sediments of the Yezo Group, the Paleogene system has a large variety of sedimentary facies We interpret this diversity as being related to the deformation of the forearc by transcurrent fault motions, which has been described on the basis of seismic interpretations. We describe significant geological events in the study area, which includes the Ishikari-Teshio Belt and forearc region of northeast Japan (Figure 1), under the same tectonic regime through the Cenozoic. Together with integrated review of basin analyses, our original geochemical data and basin modeling pave a path to the most probable tectonic history of the study area
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